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Author Topic: Affordable, budget, 85mm "IR cut" or "hot mirror"???  (Read 3217 times)
optofonik
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« on: April 23, 2013, 10:49:21 AM »
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I am wondering about the need for an IR cut filter for use with the Hitech 85mm "Master Kit".

http://preview.tinyurl.com/Hitech-Master-Kit

I'm also wondering about the incredibly high cost of an 85mm "Hot Mirror" when circular "IR cut" filters are so much more reasonably priced. I understand there is a difference between the two, in that, one one uses reflectance and the other uses filtration. I also understand that I can, at times, be woefully misinformed.

As for why I wouldn't just go for an ND with built in IR I am of the opinion that there would be times when the IR cut wouldn't be needed and so could remain undisturbed and protected in it's case. Replacing a heavily used non-IR ND in case of damage would be less than an ND/IR filter. It's sort of moot really because I can't afford ND filters with built in IR so I;m stuck with going for a separate IR cut filter.

Thanks for... wait for it...




clearing this up for me.  Grin


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Graham Welland
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« Reply #1 on: April 24, 2013, 07:31:38 PM »
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How wide do you intend to shoot with this outfit? The reason I ask is that there is a distinct difference in behaviour between various hot mirror/IR cut filters depending upon whether they use absorption or interference to do the filtering. For example, with an interference filter you may see a radial colour shift with wide angle images - I had this problem with B+W IR cut filters with 24mm or wider focal lengths. In the end I went with a Kolarivision IR hotmirror filter for my full spectrum D800.

Another thing to consider is the IR cut off point. Generally the IR cut will be at 720nm but some are higher at 680nm etc. The more expensive hotmirror filters may also be both IR and UV cut as well. You need to do some research to find out the exact characteristics. Also, IR cut filters aren't 100% neutral either so it's always worth setting either an auto_WB or custom WB when using them. (Actually the same applies to the NDs).
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Graham
optofonik
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« Reply #2 on: May 07, 2013, 12:29:50 AM »
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Thanks for the reply, Graham. Using an APS-C camera I'd like to shoot as wide as 18mm (28mm eq. in FF). As I've been researching I keep coming across the 720nm / 680nm thing; still getting my head 'round it. I'll be using Formatt 85mm filters and their aluminum holder with the 95mm circular front attachment so I'm limited to 95mm hot mirror / IR cut filter sizes for the sake of affordability. Going by your experience with the B&W it looks like my only affordable option is a filter by a company I've never heard of, Cavision.

Lots to learn, still, so thanks for the insight.
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